Involvement of alkylhydroxybenzenes, microbial autoregulators, in controlling the expression of stress regulons

Alkylhydroxybenzenes (AHB) were found to control the activation of protective functions of microorganisms by inducing stress gene expression and increasing the frequency of the intrapopulation phase transitions which are responsible for the phenotypic variability of bacteria. We established the dependence of the regulatory effects of AHB on their structure (alkyl radical length) and concentration. A reversion assay using the tryptophan auxotrophic strain Bacillus subtilis trpA5 B 1733 indicated a relationship between the reversion frequency that was 40-120 times higher than the background value and phase transition's intensity (with R → S transition rates up to 87% in contrast to 2% in the control experiment) induced by specific doses (5-100 mg/ml) of long-chain AHB such as C-AHB acting for a short time (1 h) on vegetative (dividing or stationary-phase) B. subtilis cells. Using four test strains constructed from Escherichia coli C600 thi, thr, leuΔ(pro-lac) with transcriptional or translational vectors containing the hybrid umuD-lacZ or osmE-lacZ operons, we demonstrated that AHB perform the regulatory functions involved in controlling the SOS response gene expression and the general rpoS -dependent stationary-phase regulon, respectively. The dose-dependent effect of long-chain AHB (within the 50-100 μg/ml range) resulting in a two- to threefold increase in the stress gene expression, similar to the effect of natural stress factors such as UV irradiation and starvation, provides evidence that AHB function as alarmones (danger signals). From the fact that the osm E gene is upregulated by 35-70 μg/ml C-AHB (its regulation level is increased up to twofold), it follows that C-AHB controls rpoS-dependent regulation and the transition to the stationary phase. The effect of the short-chain homologue C-AHB substantially differs from that of C-AHB. C-AHB in concentrations of 10-100μg/ml causes a significant decrease in osmE and umuD expression. A 30-min preincubation of cells with 10-100μg/ml C-AHB protected them from UV irradiation, as was observed as a 3. 6-fold decrease in umuD expression. Comparative analysis of the marker gene's expression values in the strains with the transcriptional and translational vectors demonstrates that AHB nonspecifically activate stress regulons at the transcription level. © Pleiades Publishing, Ltd., 2009.